
When a sound signal from a microphone or on a tape needs to be read into a computer, it is digitized, which means that it is sampled and quantized.
Sampling is the discretization of the time domain of the signal: each second of the signal is divided up into 11025, 22050, or 44100 slices (or any other suitable number), and a sample value is associated with each slice. For instance, a continuous 377Hz sine wave is expressed by
x(t) = sin (2π 377 t) 
If the sampling frequency (or sample rate) is 44100 Hz, this sine wave will be sampled at points spaced Δt = 1/44100 second apart, and the sample values will be
x_{i} = sin (2π 377 (t_{0} + i Δt)) 
where t_{0} is the time after which sampling begins. Δt is called the sample period.
Quantization is handled in the next section (§1.2).
© ppgb, March 30, 2004